How to hide a few objects of a multiple combined object cloth simulation?
What about adding some light force field (for example: wind) coming from the inside of the bag, just to avoid the collision of particles with the bag itself?

Here's a tutorial to manage the overlapping particles in Blender, not sure if it can help you.

You can also try to use the shader Particle Info Node, trying to identify the particle ID and setting a custom shader node (Transparent for example) for these particles.